Colourful Play-Doh like Material
Something like this might be a good start.





Two Voronoi textures are distorted by two noise textures, each Voronoi texture controls a color ramp with a few different colors. 

The results are mixed together and get even more distorted by another noise texture. The Mapping node at the start controls the general direction of the clay strains. 

Link to the .blend file: 



You can play with all the values, maybe you get even closer to what you want.